BIOLOGY 2E: Chapter 5 STRUCTURE AND FUNCTION OF PLASMA MEMBRANES

Flashcards covering key vocabulary, concepts, and processes related to the structure and function of plasma membranes, including different types of cellular transport, membrane components, and tonicity.

Fluid Mosaic Model

Proposed in 1972 by S.J. Singer and G.L. Nicolson, it describes the plasma membrane as a bilayer of phospholipids that move freely (fluid) with other molecules (proteins, cholesterol, glycoproteins, glycolipids, carbohydrates) scattered throughout (mosaic quality).

Plasma Membrane

Composed of a bilayer of phospholipids, proteins, cholesterol, glycoproteins, glycolipids, and carbohydrates, separating the internal contents of a cell from its exterior.

Phospholipid Bilayer

The structural basis of a plasma membrane, where phospholipids arrange with polar (hydrophilic) heads facing outward and hydrophobic tails facing inward.

Polar Heads (phospholipid)

The hydrophilic, phosphate-containing part of a phospholipid molecule that faces the aqueous environment on either side of the membrane.

Hydrophobic Tails (phospholipid)

The nonpolar, fatty acid chains of a phospholipid molecule that face inward, away from water, within the membrane's core.

Integral Membrane Proteins

Proteins embedded within the plasma membrane's lipid bilayer, possessing both hydrophobic and hydrophilic regions that determine their arrangement.

Glycoprotein

A protein with a carbohydrate attached, located on the exterior surface of the plasma membrane, functioning in cell-cell recognition and attachment.

Glycolipid

A lipid with a carbohydrate attached, located on the exterior surface of the plasma membrane, functioning in cell-cell recognition and attachment.

Oligosaccharide Carbohydrates (membrane)

Major components on the exterior surface of the plasma membrane, bound to either proteins (glycoproteins) or lipids (glycolipids), crucial for cell-cell recognition and attachment.

Membrane Fluidity

The property of the plasma membrane describing the free movement of its components, essential for its structure and function, affected by phospholipid type, temperature, and cholesterol.

Saturated Fatty Acids (effect on fluidity)

Phospholipids with saturated fatty acids pack together more closely, leading to a more rigid membrane.

Unsaturated Fatty Acids (effect on fluidity)

Phospholipids with unsaturated fatty acids prevent close packing, contributing to a more fluid membrane.

Cholesterol (effect on fluidity)

Located within the fatty acid layer, it acts as a fluidity buffer, maintaining membrane fluidity in cold temperatures and preventing excessive fluidity in hot temperatures.

Plasma Membrane Asymmetry

The characteristic that the inner surface of the plasma membrane differs from its outer surface, featuring specific proteins and components on each side.

Passive Transport

Transport across a membrane that does not require cellular energy, moving substances down their concentration or electrochemical gradient.

Diffusion

The simplest type of passive transport, where a substance moves from an area of high concentration down its concentration gradient until equilibrium is reached.

Concentration Gradient

The difference in concentration of a substance across a space, driving its movement during diffusion.

Equilibrium (diffusion)

The state where a substance's concentration is equal throughout an area, and net movement ceases.

Facilitated Transport (Facilitated Diffusion)

Passive transport that moves substances down their concentration gradients through transmembrane, integral membrane proteins (channel or carrier proteins).

Channel Proteins

Transmembrane integral proteins that facilitate passive transport of ions and small polar molecules by providing a hydrophilic pore; some are gated and open only upon receiving a signal.

Aquaporins

Specific channel proteins that immensely speed up the diffusion of water across the membrane.

Carrier Proteins (passive transport)

Transmembrane integral proteins that are specific to a single substance, binding to it, changing shape, and moving it across the membrane down its concentration gradient.

Osmosis

The diffusion of water across a selectively permeable membrane, moving from an area of higher water concentration to one of lower water concentration.

Selectively Permeable Membrane

A membrane that allows certain substances (like water) to pass through while restricting others (like solutes), crucial for osmosis.

Tonicity

A term describing how an extracellular solution can change the volume of a cell by affecting osmosis.

Osmolarity

The total solute concentration of a solution, including both permeable and non-permeable solutes.

Hypotonic Solution

An extracellular solution with a lower concentration of solutes compared to the cell's interior, causing water to enter the cell.

Hypertonic Solution

An extracellular solution with a higher concentration of solutes compared to the cell's interior, causing water to leave the cell.

Isotonic Solution

An extracellular solution with an equal concentration of solutes compared to the cell's interior, resulting in no net water movement.

Crenated Cell

An animal cell that has shrunken and developed a scalloped appearance due to water loss when placed in a hypertonic solution.

Lysed Cell

An animal cell that has burst due to excessive water intake when placed in a hypotonic solution.

Turgor Pressure (plant cells)

The pressure exerted by the central vacuole against the cell wall in plant cells, crucial for growth and function, achieved when cells are in a hypotonic solution.

Plasmolysis

The process in plant cells where the plasma membrane detaches from the cell wall due to water loss and shrinkage when the cell is in a hypertonic solution.

Active Transport

Transport that requires energy to move ions or molecules against their concentration gradient or electrochemical gradient.

Electrochemical Gradient

A combined gradient that arises from the difference in solute concentration and electrical charge across a membrane.

Primary Active Transport

A type of active transport where ATP hydrolysis directly provides the energy to move substances against their gradients.

Secondary Active Transport

A type of active transport that uses the energy stored in an electrochemical gradient (created by primary active transport) to move a different substance against its own gradient.

Pumps (active transport)

Transmembrane, integral carrier proteins that perform active transport.

Uniporter

A type of pump that carries one molecule or ion across the membrane.

Symporter

A type of pump that carries two different molecules or ions in the same direction across the membrane.

Antiporter

A type of pump that carries two different molecules or ions in different directions across the membrane.

Na+-K+ Pump

An example of primary active transport (an antiporter) that moves 3 Na+ ions out of the cell and 2 K+ ions into the cell using 1 ATP molecule, creating an electrochemical gradient.

Electrogenic Pump

A pump that creates a charge imbalance across the membrane, thereby contributing to the electrical potential across the membrane (e.g., Na+-K+ pump).

Bulk Transport

A type of active transport used by cells to import or export molecules or particles that are too large to pass through transport proteins, always requiring energy.

Endocytosis

A type of bulk transport where the cell imports substances by engulfing them with its plasma membrane, forming a vesicle or vacuole.

Exocytosis

A type of bulk transport where vesicles containing substances fuse with the plasma membrane to release their contents to the exterior of the cell.

Phagocytosis

Literally 'cellular eating', a type of endocytosis where the cell membrane surrounds and engulfs a large particle, forming a large vacuole, often used by immune cells.

Pinocytosis

Literally 'cellular drinking', a type of endocytosis where the cell membrane invaginates, surrounds a small volume of fluid containing dissolved substances, and pinches off to form a small vesicle.

Receptor-Mediated Endocytosis

A highly specific type of endocytosis where the uptake of a particular substance is triggered by its binding to specific receptors on the external surface of the plasma membrane, forming a coated vesicle.